1) Field
Embodiments of the present invention pertain to the field of semiconductor processing and, in particular, to methods and apparatuses for correcting the position of a substrate on a carrier ring.
2) Description of Related Art
In a processing tool substrates are transferred from a first location to a second location by wafer handling robots. For example, an atmospheric wafer handling robot in a factory interface may transfer a substrate from a front opening unified pod (FOUP) to a load lock within the processing tool. A second wafer handling robot within a portion of the processing tool under a vacuum may transfer a substrate from the load lock to a processing chamber, such as a plasma etching or deposition chamber. Both the atmospheric wafer handling robot and the vacuum wafer handling robots pick up the substrate with an end effector. When the end effector lifts the substrate up off of a supporting structure, the location of the substrate relative to the end effector is not precisely known. In order for the wafer handling robot to adjust for potential misalignment when placing the substrate at a second position, the center point of the substrate needs to be calculated.
Points along the circumference of the substrate are determined by passing the substrate through sensors and calculating a best fit circle that can be fitted to the points, thereby providing the location of the center point. However, when the substrate does not have a constant radius, center finding processes may not provide sufficient information to determine a center point of the substrate. Additionally, when the substrate is circular, such as a semiconductive wafer, the rotational orientation of the substrate is not critical for passing the substrate through an opening. In contrast, when the substrate does not have a constant diameter, the rotational orientation of the substrate becomes critical. For example, if such a substrate is improperly oriented when attempting to pass it through an opening, then the diameter of the substrate may be greater than the opening and not fit.